"It was doubly shocking because it was perpetrated by a 15-year-old boy and it underlines the importance of families, communities, leaders being very aware of whether young people are becoming radicalised," Mr Turnbull said.

He urged the community to remember the Australian Muslim community would be especially appalled by the crime.

"We must not vilify or blame the entire Muslim community with the actions of what is, in truth, a very, very small percentage of violent extremist individuals," Mr Turnbull said.